The present invention relates generally to fiber-optic systems for telecommunication and data-communication applications. More specifically, it relates to a novel type of coupling modules for interconnecting fiber-optic components.
The explosive growth of Internet traffic has imposed an unprecedented demand on the existing communications backbone-fiber-optic networks. As the demand for ever greater bandwidth grows, a particular challenge to fiber-optic equipment makers is to increase the bandwidth capacity of fiber-optic transceivers without increasing their overall physical dimensions, so that the users of the fiber-optic transceivers can attain higher bandwidth without increasing the sizes of their network switch boxes.
A crucial step in achieving greater bandwidth capacity while shrinking the package size lies in a simple and reliable way of coupling light between optoelectronic devices (e.g., lasers, light-emitting diodes, and photo-detectors) and optical fibers. This is a difficult task in a system where one or more optical fibers are brought into the proximity of optoelectronic devices by a fiber connector, for the fiber connector is typically aligned using passive alignment means which requires high precision and stringent tolerance. The task becomes more formidable when a fiber ribbon-connector is used to bring a plurality of optical fibers to an array of optoelectronic devices in a parallel fashion.
An effective way of coupling optical fibers in a fiber connector to their corresponding optoelectronic devices is to use an optical coupler that is embedded with optical lenses. The use of lenses to couple light has additional advantages of increasing the working distance and easing the mechanical tolerance imposed on the assembled components. This way of optical coupling, however, requires an accurate and reliable alignment amongst optical fibers in the fiber connector, optical lenses in the coupler, and optoelectronic devices that is to be maintained over a wide range of operating temperatures. In addition, such an optical coupler should be simple in assembly, therefore more reliable in alignment and lower in cost.
Furthermore, as the bandwidth increases, fiber-optic transceivers run at increasingly faster speeds. Accordingly, the manufacturing process for the fiber-optic transceivers has evolved from using electrical pins by way of wave solder processing to Ball Grid Array (BGA) by way of reflow processing. The latter is a surface mount technology. Given that the reflow processing typically occurs at a temperature around 220xc2x0 C., the optical coupling devices along with other optical components in a high-speed fiber-optic transceiver must be able to withstand this high-temperature treatment, while maintaining their integrity and performance.
Various devices for the interconnections of optical fibers and for the coupling of optical fibers to optoelectronic components have been devised in the art. For instance, U.S. Pat. Nos. 5,574,814, 5,671,311, and 5,781,682 disclose several optical couplers. No optical lenses, however, are incorporated in these prior art coupling devices. Although optical lenses are implemented in an optical coupler disclosed by U.S. Pat. Nos. 5,002,357, the assembly housing of this coupler also contains a fiber connector and an electronic light pulse communication device among other things, thus making it bulky and less modular.
Depicted in FIG. 1 is another prior art optical coupler that incorporates optical lenses. Optical coupler 100 comprises a transparent plastic plate 11 molded with a plurality of plastic lenses 12. Since optical coupler 100 is entirely made of transparent plastic, it will not be able to withstand the high-temperature reflow processing for BGA described above, thus rendering it not applicable to high-bandwidth fiber-optic transceivers. Moreover, given that optical coupler 100 is not equipped with any alignment features, it would be difficult to optically align optical coupler 100 with other optical elements in an accurate and secure fashion.
As fiber-optic systems rapidly grow in modern communications networks, there exists a need for simple, effective, modular, versatile, and low-cost optical coupling devices for high-bandwidth fiber-optic transceivers.
The aforementioned need in the art is provided by a coupling module for coupling light between two optical devices, such as an optical fiber connector and an optoelectronic device. In one embodiment of the present invention, a coupling module of the present invention comprises an alignment plate, one or more beam-shaping elements, and one or more alignment elements. The beam-shaping elements are embedded in one or more precision slots on the alignment plate, typically by way of press-fitting, such that their respective positions are secured within the alignment plate. The alignment elements, typically in the form of alignment pins and holes, are produced on the alignment plate in such a way that they effectively become an integral part of the alignment plate. The positions of the alignment elements are so chosen that they correspond to the alignment features on peripheral devices, such as a fiber connector and an optoelectronic device. The precision slots and alignment elements can be created in a single manufacturing process, thereby enabling the beam-shaping elements and alignment elements to be aligned in a simple, precise and secure way. Moreover, the relative physical arrangement between the beam-shaping elements and the alignment elements are configured such that once the alignment elements are engaged with the peripheral devices, accurate optical alignment between the peripheral devices and the coupling module is also attained. A coupling module thus constructed maintains a precise optical alignment that is less susceptible to change with temperature variations (e.g., during the high-temperature treatment described above) and other extraneous effects.
In an alternative embodiment of the present invention, the beam-shaping elements are embedded into the precision slots at an elevated temperature, whereby the precision slots expand and/or the alignment plate softens to allow the beam-shaping elements to be press-fit with relative ease. The use of a soft metal like copper for the alignment plate facilitates the press-fitting process. Subsequent cooling to a normal operating temperature then causes the beam-shaping elements to be compressed in their respective positions within the alignment plate. In the coupling module thus constructed, the beam-shaping elements are more firmly embedded in the alignment plate during the normal operation, thereby rendering a more enduring optical alignment.
In another embodiment of the present invention, the alignment plate is made to contain one or more xe2x80x9cplungersxe2x80x9d, comprising one or more foreign materials. The plungers are configured such that one or more gaps form between the embedded plungers and the remaining of the alignment plate, thereby providing one or more precision slots. The incorporation of the plungers in an alignment plate renders a variety of utilities and advantages. For instance, it is easier to create the precision slots by way of embedding the plungers in the alignment plate than having the precision slots directly machined out of the alignment plate, for a combined (and hence larger) area occupied by a plunger and the corresponding precision slot can be readily produced by way of stamping, or other suitable techniques. The plungers can also be of xe2x80x9cthermalxe2x80x9d type, namely, they are made of materials whose coefficients of thermal expansion are markedly different from that of the alignment plate. In this case, the alignment plate with the embedded xe2x80x9cthermal plungersxe2x80x9d are heated (or cooled) to an elevated (or lower) temperature, such that the precision slots expand to allow the beam-shaping elements to be press-fit into the precision slots with relative ease. Subsequently cooling (or warming) to a normal operating temperature causes the beam-shaping elements to be firmly compressed in their respective positions within the alignment plate. The incorporation of the xe2x80x9cthermal plungersxe2x80x9d in an alignment plate advantageously exploits the difference in coefficient of thermal expansion between different materials and thereby enables the beam-shaping elements to be more securely embedded in the alignment plate. Furthermore, the plungers can be of xe2x80x9ccompressionxe2x80x9d type, that is, they are made of a soft metal such as copper, thereby allowing the alignment plate to be made of a hard metal, such as stainless steel. An important advantage of using a hard metal for the alignment plate is that the alignment elements (e.g., alignment pins) are more firmly secured in the alignment plate and hence their respective positions are less susceptible to shift. The use of the xe2x80x9ccompression plungersxe2x80x9d permits the beam-shaping elements to be embedded in the precision slots by way of press-fitting. All in all, the use of plungers facilitate the embedding of the beam-shaping elements and enhances the overall stability of optical alignment of the coupling module thus constructed.
In the present invention, the alignment plate is typically made of a metal, such as copper, aluminum, or stainless steel. An advantage of using copper or stainless steel is that the coefficients of thermal expansion of these materials match that of the commonly used materials for making PC boards (e.g., FR4) more closely than the coefficient of thermal expansion of transparent plastic (used in the prior art optical coupler of FIG. 1) does. The alignment plate can also be made of other types of metal (e.g., brass), machinable ceramic, or high-temperature plastic (e.g., opaque plastic) The alignment elements, such as alignment pins and holes, are generally produced by means of machining, casting and stamping, such that they effectively become an integral part of the alignment plate. And the alignment elements and the precision slots can be created in a single manufacturing process. The alignment pins are typically made of metal, such as brass or stainless steel. A beam-shaping element generally refers to an optical assembly having beam-focusing and beam-shaping capabilities. It can be, for instance, a single refractive or diffractive lens, a ball lens, a GRIN lens, or other beam-focusing and beam-shaping means known in the art. It can also comprise an assembly of refractive lenses, diffractive lenses, ball lenses, and GRIN lenses arranged or molded in an array. The use of relatively simple and inexpensive lenses, e.g., glass ball lenses, eases the manufacture process and lowers the cost of the coupling module of the present invention.
It should be noted that various exemplary embodiments in this specification are provided for illustrative purposes, to elucidate the principle and the scope of the present invention. In general, an alignment plate may contain alignment elements in the form of a combination of alignment pins and alignment holes. It may also contain only alignment pins or alignment holes. There can also be situations where an alignment plate does not contain any alignment elements in the form of alignment pins or holes, but is embedded with alignment features in its body and along its edges. Those skilled in the art will know how to design an alignment plate along with appropriate alignment elements and features in accordance with the present invention, for a given application.
In yet another embodiment of the present invention, the coupling module of the present invention further contains one or more transparent windows that cover the beam-shaping elements embedded in the alignment plate. The primary function of the transparent windows is to prevent dust, moisture, and other environmental factors from degrading the performance of the embedded optics. The sealing between the transparent windows and the alignment plate need not necessarily be hermetic. The windows may further contain an optical coating (such as an anti-reflection coating) on their respective outer surfaces, or be placed with a slight tilt to reduce the optical reflection, since optical back-reflection can adversely affect the performance of a fiber-optic transceiver. If so desired, the windows can also be shaped such that they serve as auxiliary optical lenses (or the windows carry appropriate types of optical coating), so as to complement the performance of the beam-shaping elements in the coupling module of the present invention.
The coupling module of the present invention can be employed to optically couple fiber connectors and optoelectronic devices in a passive alignment, an active alignment, or a combination of both. In the passive alignment, the coupling module is equipped with alignment pins and holes designed to mate the corresponding alignment features on the peripheral devices, which may include a fiber connector on one side and an optoelectronic device on the other. In the active alignment, the coupling module is first sandwiched between first and second peripheral devices. After the optical alignment amongst the three devices is obtained, the position of the coupling module is then secured by use of an adhesive agent, such as epoxy or solder. In general, the optical alignment between a fiber connector and a coupling module is engaged in a passive manner by way of alignment pins and holes; whereas the optical alignment between a coupling module and an optoelectronic device may be adjusted actively and then secured by use of an adhesive agent. The passive alignment is generally more secure and less susceptible to extraneous effects. The active alignment, by comparison, imposes fewer physical restrictions on the coupling module and peripheral devices.
All in all, the coupling module of the present invention provides a significant simplification, size and cost reduction in the packaging of optoelectronic devices, while maintaining a more accurate and reliable optical alignment between optical fibers and optoelectronic devices. The unique design of the optical coupling module of the present invention enables it to readily withstand temperature of 220xc2x0 C. or higher while maintaining its integrity and performance, hence rendering it a desirable candidate for high-speed fiber-optic transceivers. Another advantage of the coupling module of the present invention is that it permits the use of relatively simple and inexpensive lenses, such as glass ball lenses, thereby easing the manufacture process and lowering the overall cost. A further advantage of the present invention is that the coefficient of thermal expansion of the alignment plate can be made to match that of the commonly used materials for making PC boards (e.g., FR4) more closely than the prior art optical coupler (shown in FIG. 1) is able to do. Moreover, being capable of carrying a plurality of beam-shaping elements such as an array of optical lenses, the coupling module of the present invention is particularly suited for coupling multiple optical fibers in a fiber connector to arrayed optoelectronic devices.
It should be noted that other types of optical elements, such as optical switches, filters, isolators and polarization rotators, can be embedded in a coupling module of the present invention, either in addition to or in replacement of the beam-shaping elements discussed above. Moreover, the general principle of the present invention can be applied to constructing coupling modules for coupling other types of electromagnetic radiationxe2x80x94extending beyond the optical regime of the spectrum. For instance, by incorporating appropriate beam-shaping and beam-coupling elements, a coupling module according to the present invention can be used to couple infrared, or microwave radiation.
The novel features of this invention, as well as the invention itself, will be best understood from the following drawings and detailed description.